The bodies of crew members of a Pakistani airliner that crashed in December could be exhumed for tests to determine if they were incapacitated by drugs or poisoned.

Pakistani investigators examine the wreckage of a passenger plane that crashed near Abbottabad on December 7, 2016. (AP)

The cockpit crew of a Pakistan International Airlines flight that crashed last month may have been drugged or taken intoxicants, according to reports that have added a fresh twist to the accident that killed all 47 people on board the aircraft.

The bodies of the crew of the ATR 42 aircraft, which crashed near Havelian on December 7, may be exhumed to determine if any of them was incapacitated or poisoned, reports in the local media said on Tuesday.

Islamabad district health officer Najeeb Durrani submitted a letter to the Pakistan Institute of Medical Sciences (PIMS) in Islamabad, the country’s main medical facility, suggesting the bodies be exhumed in line with the requirements of the investigation board.

The suggestion followed suspicions the crew may not have been in full control of their senses at the time of the crash. The letter also detailed the procedure for exhuming the bodies and suggested that directions were given by the senior joint director (medical) of the Civil Aviation Authority (CAA) at Benazir Bhutto International Airport.

Durrani said the letter was part of standard operating procedures in all such air crash investigations.

PIMS administrator Altaf Hussein confirmed receiving the letter on Monday and said exhumation may not be necessary as the hospital’s administration had collected samples from the bodies of crew members that can be used to test for drugs.

But investigators have insisted on exhumation, which the PIMS’ administration has resisted so far. “This will be done after orders are received from the deputy commissioner as orders (for) exhuming a body can only be given by him,” Hussein said.

All passengers on board flight PK-661 were killed, including 31 men, nine women, two infants and five crew members. Among the dead was well known pop musician-turned-evangelist Junaid Jamshed.

Earlier, the CAA shared its findings from the black box data of the ill-fated flight with the Senate Standing Committee on Rules of Procedures and Privileges. In a statement, CAA secretary Irfan Elahi said both engines of the plane were working at “100%” when it took off from Chitral for Islamabad.

However, only one engine was running when the aircraft crashed. According to the black box data, no action was taken to land the plane before the crash, he said.

Elahi said investigations were underway to ascertain why the plane crashed when one of its engines was still working. The pilot was “calm” when he made his first call to the control room at 4:12 pm.

But the pilot issued a May Day call two minutes later, stating one of the engines was not running. The pilot’s last communication was recorded at 4:17 pm and after 10 to 15 minutes, it was reported the plane had crashed.

Following the crash, PIA chairman Azam Saigol resigned, citing personal reasons as the reason for his decision. Pressure for his resignation grew after there was a hue and cry, especially on social media, against PIA for not maintaining its planes in line with international standards.